Lubricant composition



atented Fe. g, W43

LUBRICANT COIWPO SITKON New York No Drawing. Application September 21, 1940, Serial No. 357,750

' 4 Claims.

This invention has to do with lubricating oils and is more particularly concerned with the stabilization of viscous mineral oils of the lubricant type by adding thereto a minor proportion of an addition agent which will inhibit the deleterious efiects of oxidation upon such-oils under the conditions normally encountered in their use.

Lubricants of the type used in internal combustion engines, such as motor oils used in automobile crankcases, and especially those refined by certain solvent-extraction methods, tend to oxidize when subjected to high temperatures and form products that are corrosive to bearing metals. This corrosive action may be severe with certain bearing metals, particularly those having the corrosion susceptibility of cadmium-silver alloys, and may cause their failure within a comparatively short time. It is one object of this invention to provide a lubricant composition which would normally be corrosive to bearing metals of'this type, but in which such corrosive action is inhibited by one or more of a novel class of addition agents.

Also, highly refined oils of the type used in transformers, under the conditions encountered in use, tend to form relatively large amounts of acidic constituents as a result of oxidation. The formation of acidic bodies is highly undesirable for most applications of the oil. For example, when the oil is used as an insulating or cooling medium in electrical equipment such as transformers or capacitors, an increase in acidic bodies results, which tends to lower the dielectric strength of the oil and has other harmful effects which are undesirable. These acids are corrosive to metals and thus reduce the useful life of the oils as lubricants or for other purposes in which they come in contact with metals. These acidic materials are also injurious in textile lubricants and in spray oils. It is a-further object of this invention to provide highly refined oils of the aforesaid type in which the develop ment of acidic products of oxidation is inhibited by a minor proportion of this novel addition agent.

This invention is predicated upon the discovery that a triarylmethyl thiocyanate, when incorporated in a viscous mineral oil of the lubricant type, is highly effective as an inhibitor of the deleterious effects of oxidation on the oil. We are aware of the fact that the general class of aliphatic and aromatic mono-thiocyanates and iso-thiocyanates has been proposed for use as addition agents for lubricating oils. We have found that the general class of aliphatic and aromatic monothiocyanates and isothiocyanates is, at most, only slightly positive in its efiectlveness to inhibit corrosion in motor oils and to inhibit the development of acidicproducts in highly refined oils. We have discovered, however, that the triarylmethyl thiocyanates are of outstanding efiectiveness in this regard. This discovery was unexpected and unpredictable on the basis of the results observed in connection with the other thlocyano compounds disclosed in the prior art as typifying this general class.

The triarylmethyl thiocyanates are compounds having the general formula R1 (E-SCN in which R1, R2 and Ra represent abe same or different aromatic radicals. Methods for their preparation may be found in theliterature and are illustrated by the following example.

EXAMPLE I Triphenylmethyl thiocyanate was synthesized by the method of .Biilmann and Due (BuIL Soc. Chim. (4) 35390 (1924)) as follows:

Thirty grams of potassium thiocyanate were dissolved in 50 cc. of water and added with shaking to a chilled mixture of 25 cc. conc. sulfuric acid and 75 grams of ice. To this solution was added 150 cc. of ether and agitation continued for five minutes. At the end of this time the layers were allowed to separate and the aqueous layer discarded. The ethereal layer was dried rapidly by filtration through paper, treating twice with 10 gram portions of anhydrous sodium 'sulfate for ten minutes, and filtered again. To this dried solution of thiocyanic acid was added gradually 20 grams of solid triphenylmethyl chloride. Hydrogen chloride was evolved immediately, and copious quantities of white crystals-separated from the solution. The reaction mixture was allowed tostand at room temperatureffor three quarters of anhour, the

product was then, removed .by filtration and washed twice with 20 cc. portions of ether and air-dried. The melting point of the crude product thus obtained was 133-137 0., and this product was used without further purification.

Following this same general procedure, alphanaphthyl-diphenyl methyl thiocyanate was prepared from alpha naphthyl diphenylmethyl chloride. This compound was obtained as a. white'crystalline product having a melting point of 138.5 to O.

To demonstrate the effectiveness of triarylmethyl thiocyanates as addition agents for viscous mineral oils and their superiority over the general class of aliphatic and aromatic monothiocyanates, the following examples are given. In these examples the triarylmethyl thiocyanates are typified by triphenylmethyl thiocyanate and alpha-naphthyl diphenylmethyl thiocyanates. For the purpose of comparing the effectiveness of the narrow class of compounds contemplated herein with the general class of thiocyanates and isothiocyanates, we have included in these examples as compounds typifying the general class: o-tolyl isothiocyanate, alpha-naphthyl isothiocyanate, n-butyl thiocyanate and allyl isothiocyanate.

EXAMPLE II (Motor oil test) The oil used in this test was a commercial S. A. E. 20 solvent-refined motor oil. In carrymg out the test, a section of a bearing containing a cadmium-silver alloy surface and weighing about 6.0 grams was placed in a 30-gram sample of the oil (or oil blend), and the sample was maintained at a temperature of 175 C. for a period of 22 hours while a stream of air was bubbled therethrough against the surface of the bearing. The weight loss in milligrams of the bearing is interpreted as a measure of the corrosiveness of the oil. In each case a sample of the oil containing the addition agent was run concurrently with a sample of the oil alone. Each sample contained a section cut from the same bearing. The results obtained are set forth in Table I below. from which it will be observed that the triarylmethyl thiocyanates are of outstanding superiority over the other thiocyanate-s and isothiocyanates.

EXAMPLE 111 v (Highly refined oil) The oil used in this test was a very highly refined oil of the type suitable for use in transiormers. flash point of 310 F., and S. U. viscosity of 69 seconds at 100 F. The test involved heating the oil samples to a temperature of 120 C. and bubbling oxygen gas therethrough for a period of 70 hours. Neutralization numbers (N. N.) were obtained as a measure of the acidic products formed. The results are recorded in Table II below. Here again, it will be observed that the triarylmethyl thiocyanate is of outstanding superiority over the general class.

Table 11 Addition agent Weight N. N.

Per cent None 20-25 Tnphenylmethyl thloeyanatc.. 0. l 0. 58

o-Tolyl isothlocyanate 0. l0 6.

Alpha-naphthyl isothiocyanata. 0. 4. 4

-n-Butyl thiocyanate 0.10 15.4

Allyl isothiocyanate .l 0. l0 2. 4 a

The amount of addition agent used in the oil may be varied depending upon the character of the oil and the conditions encountered in use. In general it appears that the desired results may be obtained with an amount ranging from about 0.05 per cent to about 2.0 per cent.

It is to be understood that while we have illustrated the invention with certain specific examples, the scope of the invention is not limited thereby but includes such changes or modifications as fairly come within the spirit of the appended claims.

We claim:

I. A lubricating oil which normally develops products corrosive to bearing metals having the corrosion-susceptibility of cadmium-silver alloys under the conditions encountered in internal combustion engines and in admixture therewith a minor proportion of a thiocyanate having the general formula R1 l-SON wherein R1, R2 and R3 represent aromatic hydrocarbon radicals, said compound being present in It had a specific gravity of 0.871, a

- methyl thiocyanate in an an amount suilicient to inhibit said corrosive action.

2. A lubricating oil which normally develops products corrosive to bearing metals having the corrosion susceptibility of cadmium-silver alloys under the conditions encountered in internal combustion engines, and in admixture therewith a minor proportion of a triaryl methyl thiocyanate in an amount sufficient to inhibit said corrosive action.

. 3. A lubricating oil which normally develops products corrosive to hearing metals having the corrosion susceptibility of cadmium-silver alloys under the conditions encountered in internal combustion engines, and in admixture therewith a minor proportion of triphenylmethyl thiocyanate in an amount suflicient to inhibit said corrosive action.

4. A lubricating oil which normally develops products corrosive to bearing metals having the corrosion susceptibility of cadmium-silver alloys under the conditions encountered in internal combustion engines, and in admixture therewith a minor proportion of alpha-naphthyl-diphenylamount suflicient to inhibit said corrosive action.

- DARWIN BADERTSCHER.

GEORGE S. CRANDALL. FRANCIS M. SEGER. 

